Gas chromatography is a process typically used to separate volatile organic compounds. Gas chromatographs typically include ports for injection of the sample organic compounds attached to a chromatograph oven containing a column which separates the sample organic compound. Sample valves are generally used at the injection ports to precisely control and measure the samples to be injected.
The valves typically used in process gas chromatographs involve several precision machined parts. Most of the surfaces for these machined parts require some lapping to obtain a suitable flatness and then polishing to provide the necessary surface finish which will seal against a diaphragm material typically within the sample valve. The suitable polishing of machined surfaces of the valve must be performed for even the most simple air activated type valves, in which a diaphragm is the only moving part. In particular, in these valves the mating metal surfaces must be flat to provide the necessary sealing surface against the diaphragm. The diaphragm is usually made of Teflon®. Generally, the flatness required for the valves is approximately 2 lightbands over the surface of the diaphragm.
However, the more an item is polished, the more the desired flatness can be disrupted. Therefore a tradeoff is involved, and can result in a substantial cost incurred for each machined piece. Other prior art solutions for dealing with this tradeoff resulted in valve designs with larger tolerances for a less critical surface on the mating surfaces by utilizing an elastomeric type material for the diaphragm which provides the required sealing on the rougher surfaces. However, the diaphragm using elastomeric type materials allow more permeation of gases than Teflon diaphragms, or are not as inert. Depending on the application of the gas chromatograph, this can sometimes result in erroneous detection at the chromatograph oven.
Therefore there is a need for a sample valve for a chromatograph that is easier to manufacture and less costly.